Patent application title: ZOOM LENS

Abstract:

A zoom lens including, in a sequence from an object side, a first lens
group having a positive refractive power, a second lens group having a
negative refractive power, and a succeeding lens group having an overall
positive refractive power, and having a high zoom magnification and a
compact size.

Claims:

1. A zoom lens comprising, in a sequence from an object side:a first lens
group having a positive refractive power;a second lens group having a
negative refractive power; anda succeeding lens group having an overall
positive refractive power,wherein:during zooming from a wide angle
position to a telephoto position, an interval between the first lens
group and the second lens group increases, and an interval between the
second lens group and the succeeding lens group decreases;the first lens
group comprises at least one negative lens and at least three positive
lenses, and the second lens group comprises, in a sequence from the
object side, a front group having a negative refractive power and a rear
group having a positive refractive power; andthe zoom lens satisfies at
least one of the following expressions:0<R2al/R2bf<1;
and0.01<R2al/ft<0.25,where R2al denotes a radius of curvature of a
lens closest to an image side in the front group of the second lens
group, R2bf denotes a radius of curvature of a lens closest to the object
side in the rear group of the second lens group, and ft denotes an
overall focal length of the zoom lens at the telephoto position.

2. The zoom lens of claim 1, wherein at least one of the at least three
positive lenses of the first lens group has an Abbe's number of 80 or
greater.

3. The zoom lens of claim 1, wherein the at least one negative lens is
arranged closest to the object side of the first lens group.

4. The zoom lens of claim 1, wherein the front group of the second lens
group comprises two negative lenses and the rear group of the second lens
group comprises a positive lens and a negative lens arranged in a
sequence from the object side.

5. The zoom lens of claim 4, wherein the positive lens and the negative
lens of the rear group of the second lens group are formed as a doublet
lens.

6. The zoom lens of claim 1, wherein when a focal length of the first lens
group is f1 and a focal length of the second lens group is f2, the zoom
lens satisfies at least one of the following
expressions:0.2<f1/ft<0.43; and0.02<|f2/ft|<0.06.

7. The zoom lens of claim 1, wherein the succeeding lens group comprises,
in a sequence from the object side, a third lens group having a positive
refractive power and a fourth lens group having a positive refractive
power.

8. The zoom lens of claim 7, wherein during zooming from a wide angle
position to a telephoto position, the second lens group and the fourth
lens group are moved.

9. The zoom lens of claim 8, wherein during zooming from a wide angle
position to a telephoto position, the first lens group and the third lens
group are fixed.

10. The zoom lens of claim 7, wherein during zooming from a wide angle
position to a telephoto position, the first lens group and the third lens
group are fixed.

11. The zoon lens of claim 7, wherein during zooming from a wide angle
position to a telephoto position, at least one of the second lens group
and the fourth lens group are moved.

12. The zoom lens of claim 11, wherein during zooming from a wide angle
position to a telephoto position, the first lens group and the third lens
group are fixed.

14. The zoom lens of claim 7, wherein when a focal length of the third
lens group is fb3 and a focal length of the fourth lens group is fb4, the
zoom lens satisfies at least one of the following
expressions:0.15<fb3/ft<0.31; and0.07<fb4/ft<0.17.

15. A zoom lens comprising, in a sequence from an object side:a first lens
group having a positive refractive power and comprising a plurality of
positive lenses and at least one negative lens;a second lens group having
a negative refractive power and comprising at least one positive lens and
at least one negative lens; anda succeeding lens group having an overall
positive refractive power and comprising at least one positive
lens,wherein, during zooming from a wide angle position to a telephoto
position, an interval between the first lens group and the second lens
group increases, and an interval between the second lens group and the
succeeding lens group decreases.

16. The zoom lens of claim 15, wherein a number of the plurality of
positive lens of the first lens group is at least three (3), andwherein
the at least one negative lens of the first lens group is arranged
closest to the object side of the first lens group.

17. The zoom lens of claim 16, wherein the second lens group comprises, in
a sequence from the object side, a front group having a negative
refractive power and a rear group having a positive refractive power,
andwherein the front group comprises at least two negative lenses and the
rear group comprises at least one positive lens and at least one negative
lens in a sequence from the object side.

18. The zoom lens of claim 15, wherein the second lens group comprises, in
a sequence from the object side, a front group having a negative
refractive power and a rear group having a positive refractive power,
andwherein the front group comprises at least two negative lenses and the
rear group comprises at least one positive lens and at least one negative
lens in a sequence from the object side.

19. The zoom lens of claim 18, wherein the zoom lens satisfies at least
one of the following expressions:0<R2al/R2bf<1;
and0.01<R2al/ft<0.25,where R2al denotes a radius of curvature of a
lens closest to an image side in the front group of the second lens
group, R2bf denotes a radius of curvature of a lens closest to the object
side in the rear group of the second lens group, and ft denotes an
overall focal length of the zoom lens at the telephoto position.

20. The zoom lens of claim 15, wherein at least one of the plurality of
the positive lenses of the first lens group has an Abbe's number of 80 or
greater.

Description:

CROSS-REFERENCE TO RELATED PATENT APPLICATION

[0001]This application claims priority from Korean Patent Application No.
10-2009-0047575, filed on May 29, 2009, the disclosure of which is
incorporated herein in its entirety by reference.

BACKGROUND

[0002]1. Field

[0003]Apparatuses consistent with the present invention relate to a zoom
lens having a high zoom magnification.

[0004]2. Description of the Related Art

[0005]Digital cameras, video cameras, monitoring cameras that have solid
state pickup devices, such as charge coupled devices (CCDs) or
complementary metal-oxide semiconductors (CMOSs), are used widely.
Imaging optical apparatuses for use in these cameras are required to be
compact, lightweight, and inexpensive. In addition, demand for imaging
optical apparatuses providing a high zoom magnification has increased.

SUMMARY

[0006]According to one or more exemplary embodiments, there is provided a
zoom lens having a high zoom magnification and properly-corrected
aberration.

[0007]According to an exemplary embodiment, there is provided a zoom lens
including, in a sequence from an object side: a first lens group having a
positive refractive power; a second lens group having a negative
refractive power; and a succeeding lens group having an overall positive
refractive power. During zooming from a wide angle position to a
telephoto position, an interval between the first lens group and the
second lens group increases, and an interval between the second lens
group and the succeeding lens group decreases. The first lens group
includes at least one negative lens and at least three positive lenses,
and the second lens group includes, in a sequence from the object side, a
front group having a negative refractive power and a rear group having a
positive refractive power; and the zoom lens satisfies at least one of
the following expressions:

0<R2al/R2bf<1; and

0.01<R2al/ft<0.25,

[0008]where R2al denotes a radius of curvature of a lens closest to an
image side in the front group of the second lens group, R2bf denotes a
radius of curvature of a lens closest to the object side in the rear
group of the second lens group, and ft denotes an overall focal length of
the zoom lens at the telephoto position.

[0009]According to an exemplary embodiment, at least one of the at least
three positive lenses of the first lens group may have an Abbe's number
of 80 or greater.

[0010]According to an exemplary embodiment, the at least one negative lens
may be arranged closest to the object side of the first lens group.

[0011]According to an exemplary embodiment, the front group of the second
lens group may include two negative lenses and the rear group of the
second lens group may include a positive lens and a negative lens
arranged in a sequence from the object side.

[0012]According to an exemplary embodiment, the positive lens and the
negative lens of the rear group of the second lens group may be formed as
a doublet lens.

[0013]According to an exemplary embodiment, when a focal length of the
first lens group is f1 and a focal length of the second lens group is f2,
the zoom lens satisfies the following expressions:

0.2<f1/ft<0.43

0.02<|f2/ft|<0.06.

[0014]According to another exemplary embodiment of the present invention,
the succeeding lens group may include, in a sequence from the object
side, a third lens group having a positive refractive power and a fourth
lens group having a negative refractive power.

[0015]According to another exemplary embodiment of the present invention,
during zooming from a wide angle position to a telephoto position, the
second lens group and the fourth lens group may be moved.

[0016]According to another exemplary embodiment of the present invention,
during zooming from a wide angle position to a telephoto position, the
first lens group and the third lens group may be fixed.

[0017]According to another exemplary embodiment of the present invention,
the fourth lens group may perform focusing.

[0018]According to another exemplary embodiment of the present invention,
when a focal length of the third lens group is fb3 and a focal length of
the fourth lens group is fb4, the zoom lens satisfies at least one the
following expressions:

0.15<fb3/ft<0.31; and

0.07<fb4/ft<0.17.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]The above and other aspects of the present inventive concept will
become more apparent by describing in detail exemplary embodiments
thereof with reference to the attached drawings, in which:

[0020]FIGS. 1A, 1B and 1C are cross-sectional views of a zoom lens,
according to an exemplary embodiment, at a wide angle position, a middle
position, and a telephoto position;

[0021]FIGS. 2A, 2B and 2C illustrate longitudinal spherical aberration,
astigmatic field curvature, and distortion of the zoom lens of FIG. 1 at
the wide angle position, the middle position, and the telephoto position,
respectively, according to an exemplary embodiment;

[0022]FIGS. 3A, 3B and 3C are cross-sectional views of a zoom lens,
according to an exemplary embodiment, at a wide angle position, a middle
position, and a telephoto position;

[0023]FIGS. 4A, 4B and 4C illustrate longitudinal spherical aberration,
astigmatic field curvature, and distortion of the zoom lens of FIGS. 3A,
3B and 3C at the wide angle position, the middle position, and the
telephoto position, respectively, according to an exemplary embodiment;

[0024]FIGS. 5A, 5B and 5C are cross-sectional views of a zoom lens,
according to an exemplary embodiment, at a wide angle position, a middle
position, and a telephoto position;

[0025]FIGS. 6A, 6B and 6C illustrate longitudinal spherical aberration,
astigmatic field curvature, and distortion of the zoom lens of FIGS. 5A,
5B and 5C at the wide angle position, the middle position, and the
telephoto position, respectively, according to an exemplary embodiment;

[0026]FIGS. 7A, 7B and 7C are cross-sectional views of a zoom lens,
according to an exemplary embodiment, at a wide angle position, a middle
position, and a telephoto position; and

[0027]FIGS. 8A, 8B and 8C illustrate longitudinal spherical aberration,
astigmatic field curvature, and distortion of the zoom lens of FIGS. 7A,
7B and 7C at the wide angle position, the middle position, and the
telephoto position, respectively, according to an exemplary embodiment.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0028]The present inventive concept will now be described more fully with
reference to the accompanying drawings, in which exemplary embodiments
are shown.

[0029]FIG. 1 is a cross-sectional view of a zoom lens, according to an
exemplary embodiment, at a wide angle position, a middle position, and a
telephoto position. Referring to FIG. 1, the zoom lens according to the
present exemplary embodiment may include a first lens group G1 having a
positive refractive power, a second lens group G2 having a negative
refractive power, and a succeeding lens group GB having an overall
positive refractive power. The lens groups G1, G2, and GB are
sequentially arranged from an object side O to an image side I.

[0030]When zooming is performed from the wide angle position to the
telephoto position, a distance between the first lens group G1 and the
second lens group G2 increases, and a distance between the second lens
group G2 and the succeeding lens group GB decreases.

[0031]The first lens group G1 may include a negative lens and at least
three positive lenses. The second lens group G2 may include, in a
sequence from the object side O, a front group G2-1 having a negative
refractive power and a rear group G2-2 having a positive refractive
power.

[0032]When the zoom lens has a high zoom magnification, large spherical
aberration occurs in the first lens group G1 at the telephoto position,
and thus, correcting spherical aberration of the entire zoom lens is
difficult. Accordingly, the first lens group G1 includes at least three
positive lenses in order to distribute positive refractive power, thereby
suppressing generation of spherical aberration. In addition, the first
lens group G1 includes at least one negative lens in order to suppress
generation of spherical aberration in the first lens group G1, thereby
facilitating correction of spherical aberration generated at the
telephoto position. Moreover, when the negative lens is arranged on the
object side O of the first lens group G1, spherical aberration may be
efficiently corrected.

[0033]The front group G2-1 of the second lens group G2 may include at
least two negative lenses on the object side O. The rear group G2-2 of
the second lens group G2 may include a positive lens and a negative lens
in a sequence from the object side O. The positive lens and the negative
lens of the rear group G2-2 may be formed as a doublet lens.

[0034]At least two negative lenses of the front group G2-1 of the second
lens group G2 are arranged closest to the object side O, whereby
correction of negative distortion at the wide angle position becomes
easier. In addition, a positive lens and a negative lens are arranged in
a sequence from the object side O in the rear group G2-2 of the second
lens group G2, whereby generation of spherical aberration in the second
lens group G2 is suppressed, and thus, variation of spherical aberration
caused during zooming may be reduced.

[0035]The zoom lens according to an exemplary embodiment may be configured
to satisfy at least one of the following Expressions 1 and 2:

0<R2al/R2bf<1 [Expression 1]

0.01<R2al/ft<0.25, [Expression 2]

where R2al denotes the radius of curvature of a lens closest to the image
side I in the front group G2-1 of the second lens group G2, R2bf denotes
the radius of curvature of a lens closest to the object side O in the
rear group G2-2 of the second lens group G2, and ft denotes an overall
focal length of the zoom lens at the telephoto position.

[0036]By satisfying the condition of Expression 1, an air lens between the
front and rear groups G2-1 and G2-2 of the second lens group G2 may have
a negative refractive power, and the negative refractive power may be
appropriately distributed in the second lens group G2. In addition,
generation of spherical aberration in the second lens group G2 is
suppressed, and thus, the variation of the spherical aberration caused
during zooming may be reduced.

[0037]When R2al/ft satisfies the condition of Expression 2, negative
spherical aberration generated due to R2al may be suitably set, and thus,
the spherical aberration in the second lens group G2 is suppressed.
Accordingly, variation of spherical aberration caused during zooming may
be reduced. In addition, since the negative refractive power in the front
group G2-1 of the second lens group G2 may be appropriately distributed,
correcting negative distortion generated at the wide angle position
becomes easy.

[0038]The zoom lens according to an exemplary embodiment may be configured
to satisfy at least one of the following Expressions 3 and 4:

0.6<R2al/R2bf<0.85 [Expression 3]

0.03<R2al/ft<0.1 [Expression 4]

[0039]The first lens group G1 may include at least one positive lens
having an Abbe's number of 80 or greater. This facilitates correction of
longitudinal chromatic aberration generated at the telephoto position.
For example, the first lens group may include at least two positive
lenses having an Abbe's number of 80 or greater.

[0040]The zoom lens according to an exemplary embodiment may be configured
to satisfy at least one of the following Expressions 5 and 6:

0.2<f1/ft<0.43 [Expression 5]

0.02<|f2/ft|<0.06 [Expression 6]

[0041]Expression 5 represents the ratio of a focal length f1 of the first
lens group G1 to the focal length ft at the telephoto position, and, when
Expression 5 is satisfied, correcting spherical aberration at the
telephoto position becomes easy, and an overall optical length may be
easily reduced.

[0042]Expression 6 represents the ratio of a focal length f2 of the second
lens group G2 to the focal length ft at the telephoto position, and, when
|f2/ft| is greater than the lower limit, correcting negative distortion
at the wide angle position becomes easy. When |f2/ft| is greater than the
upper limit, the amount of movement of the second lens group G2 required
for zooming may be reduced, thereby miniaturizing an optical system.

[0043]The zoom lens according to an exemplary embodiment may be configured
to satisfy at least one of the following Expressions 7 and 8:

0.23<f1/ft<0.35 [Expression 7]

0.03<|f2/ft|<0.045 [Expression 8]

[0044]The succeeding lens group GB may include, in a sequence from the
object side O, a third lens group G3 having a positive refractive power
and a fourth lens group G4 having a positive refractive power. Reference
numeral 20 denotes a filter.

[0045]According to an exemplary embodiment, when the zoom lens according
to the above exemplary embodiments is zoomed from the wide angle position
to the telephoto position, the fourth lens group G4 may be moved. Due to
this zooming, which is performed by the fourth lens group G4, a change in
the position of an image plane according to zooming may be reduced.

[0046]Alternatively, according to an exemplary embodiment, when the zoom
lens according to the above exemplary embodiments is zoomed from the wide
angle position to the telephoto position, the first lens group G1 and the
third lens group G3 may be fixed and the second lens group G2 and the
fourth lens group G4 may be moved. Accordingly, the structure of a lens
moving mechanism may be simplified, and the entire optical system
including the zoom lens may be miniaturized. During the zooming from the
wide angle position to the telephoto position, the interval between the
first lens group G1 and the second lens group G2 may increase, and the
interval between the second lens group G2 and the third lens group G3 may
decrease. In addition, according to an exemplary embodiment, during the
zooming from the wide angle position to the telephoto position, the
interval between the third lens group G3 and the fourth lens group G4 may
have a locus that is concave toward the image side I.

[0047]According to an exemplary embodiment, the third lens group G3 may
include a stop ST. According to an exemplary embodiment, the fourth lens
group G4 may perform focusing. When the fourth lens group G4 performs
focusing, zooming and focusing may be performed using the same lens
moving mechanism, so that the structure of the mechanism may be
simplified and the entire zoom lens may be compact.

[0048]The zoom lens according to an exemplary embodiment may be configured
to satisfy at least one of the following Expressions 9 and 10:

0.15<fb3/ft<0.31 [Expression 9]

0.07<fb4/ft<0.17 [Expression 10]

[0049]Expression 9 represents the ratio of a focal length fb3 of the third
lens group G3 to the focal length ft at the telephoto position, and, by
satisfying Expression 9, securing a back focal length may become easier,
and correcting coma may also become easier.

[0050]Expression 10 represents the ratio of the focal length fb4 of the
fourth lens group G4 to the focal length ft at the telephoto position. By
satisfying Expression 10, it may become easy to correct variation in
astigmatic field curvature that occurs during focusing, and the amount of
movement of lenses required for focusing on a very close location may be
reduced, thereby miniaturizing the moving mechanism.

[0051]The zoom lens according to an exemplary embodiment may be configured
to satisfy at least one of the following Expressions 11 and 12:

0.18<fb3/ft<0.28 [Expression 11]

0.08<fb4/ft<0.14 [Expression 12]

[0052]The term "aspherical (surface)" described in the exemplary
embodiments of the present inventive concept is defined as follows.

[0053]When the direction of the optical axis is set to be an x axis
direction, a direction perpendicular to the optical axis direction is set
to be a y axis direction, and a proceeding direction of a light beam is
set to be a forward direction, an aspherical shape of a zoom lens
according to an exemplary embodiment may be expressed as Expression 13:

where x denotes the distance from an apex of the lens along the x axis, y
denotes the distance from the apex of the lens along the y axis, K
denotes a conic constant, A4, A6, A8, and A10 denote
aspherical coefficients, and c denotes a reciprocal (1/R) of the radius
of curvature of the apex of the lens.

[0054]Detailed data about zoom lenses according to several exemplary
embodiments will now be described.

[0055]Hereinafter, f is referred to as the overall focal length of the
entire zoom lens, Fno is referred to as the F number, 2ω is a
viewing angle, R is referred to as the radius of curvature, D is referred
to as a center thickness of a lens or an interval between lenses, nd is
referred to as a refractive index, vd is referred to as an Abbe's number,
ST is referred to as a stop, and D1, D2, D3, and D4 are variable
distances.

Embodiment 1

[0056]FIGS. 1A, 1B and 1C illustrate zoom lenses, according to an
exemplary embodiment, at a wide angle position, a middle position, and a
telephoto position.

[0059]FIGS. 2A, 2B and 2C illustrate longitudinal spherical aberration,
field curvature, and distortion of the zoom lens of FIGS. 1A, 1B and 1C
at the wide angle position, the middle position, and the telephoto
position, respectively. Tangential field curvature (T) and sagittal field
curvature (S) are illustrated as the field curvature.

Embodiment 2

[0060]FIGS. 3A, 3B and 3C illustrate zoom lenses, according to another
exemplary embodiment, at a wide angle position, a middle position, and a
telephoto position.

[0063]FIGS. 4A, 4B and 4C illustrate longitudinal spherical aberration,
field curvature, and distortion of the zoom lens of FIGS. 3A, 3B and 3C
at the wide angle position, the middle position, and the telephoto
position, respectively.

Embodiment 3

[0064]FIGS. 5A, 5B and 5C illustrate zoom lenses, according to another
exemplary embodiment, at a wide angle position, a middle position, and a
telephoto position.

[0067]FIGS. 6A, 6B and 6C illustrate longitudinal spherical aberration,
field curvature, and distortion of the zoom lens of FIGS. 5A, 5B and 5C
at the wide angle position, the middle position, and the telephoto
position, respectively.

Embodiment 4

[0068]FIGS. 7A, 7B and 7C illustrate zoom lenses, according to another
exemplary embodiment, at a wide angle position, a middle position, and a
telephoto position.

[0071]FIGS. 8A, 8B and 8C illustrate longitudinal spherical aberration,
field curvature, and distortion of the zoom lens of FIGS. 7A, 7B and 7C
at the wide angle position, the middle position, and the telephoto
position, respectively.

[0073]A zoom lens according to the above exemplary embodiments may have a
high zoom magnification of 35× to 45× and allow aberration to
be properly corrected. The zoom lens according to the above exemplary
embodiments may be used in photographing optical systems, such as
monitoring cameras, camcorders, and digital cameras. The zoom lens
according to the above exemplary embodiments is compact and easily
manufactured and has a high zoom magnification and excellent performance.

[0074]While the present inventive concept has been particularly shown and
described with reference to the exemplary embodiments thereof, it will be
understood by those of ordinary skill in the art that various changes in
form and details may be made therein without departing from the spirit
and scope of the present inventive concept as defined by the following
claims.